Winter nitrogen fertilization of loblolly pine seedlings

Loblolly pine (Pinus taeda L.) seedlings were nitrogen fertilized during winter in a bare root forest tree nursery located in the coastal plain of the southeastern United States. Total application rates were 0, 50, 100, and 200 kg/N/ha applied in split applications 4 weeks apart in January and February. Seedlings were lifted and outplanted in March, 4 weeks after the second fertilization and measured at 3 and 6 months after outplanting. No seedling morphological differences were encountered at the time of lifting and outplanting although seedling shoot nitrogen content was 28% greater in the highest fertilization treatment compared to the check. Shoot nitrogen concentrations fell after outplanting regardless of treatment, decreasing from an average of 1.51% across all treatments at the time of planting to 0.64% at 6 months after planting. When measured at 6 months after outplanting, seedling dry weight and height growth after planting was shown to increase by 12% and 24%, respectively, for the high nitrogen treatment. This and other studies across a variety of sites have found positive post-outplanting seedling growth response after nutrient loading in the nursery.     

Ethylene production by loblolly pine seedlings associated with water stress

Effects of water stress on production of ethylene and its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), by loblolly pine ( Pinus taeda L.) seedlings from a Texas drought-hardy and a Virginia Coastal Plain source were investigated. Ethylene production rates in needles from the Virgnia source increased slightly with initial stress (-1.3 MPa), declined until water potential reached -1.6 MPa and then increased sharply at -2.5 MPa. The ethylene production rates in needles from the Texas also increased slightly with initial stress, then decreased with decreasing water potential. Ethylene production by root tissue was two to three times higher than needle tissue and decreased with decreasing water potential. ACC concentrations in needles of both seed sources decreased as water potential began decreasing. Below -1.4 MPa, ACC levels started increasing (Texas source) or remained constant until -2.8 MPa (Virginia source) at which time its level increased three-fold. Mean ACC levels in root tissue [122 nmol (g dry weight)⁻¹] were slightly higher than the mean levels in the needle tissue [92 nmol (g dry weight) ⁻¹]; roots apparently were more efficient in converting it to ethylene since ethylene production was two to three times higher than needle tissue. The modulation of ethylene synthesis by ACC synthase and ethyleneforming enzyme appeared to be influenced by stress level, organ and seed source.     

Mycorrhiza development of loblolly pine seedlings in relation to soil reaction and the supply of nitrate

Summary A study was made of the relative influence of nitrate and soil pH on mycorrhiza development in seedlings of loblolly pine (Pinus taeda L.). The investigation was conducted in the greenhouse, using as the growth medium topsoil collected from a young pine plantation.Lime-induced Fe-deficiency occurred at pH 7.5, resulting in chlorotic seedlings with few mycorrhizas. Chlorosis was corrected, and normal mycorrhiza development restored, by adding Fe-EDTA without altering soil pH.Application of 18 1/2, 37, and 74 pounds of N per acre as NaNO₃ reduced mycorrhiza development at age 21 weeks, but had no effect at age 45 weeks. At 21 weeks, the degree of infection varied inversely as the percentage total N in seedling roots. The effect of NaNO₃ was due to the nitrate ion, since Na₂CO₃ did not reduce mycorrhiza development even though it raised soil pH.Alkalinityper se did not affect mycorrhiza formation in loblolly pine seedlings, but only indirectly through its influence on host nutrition. Normal mycorrhiza development was possible at pH values of 7.2 and 7.5, provided Fe deficiency was corrected, and soil nitrate level was kept low. The results may be interpreted in terms of the carbohydrate — nitrogen balance in the root tissues.     

Effect of carbon dioxide, fertilization and irrigation on loblolly pine branch morphology

 Foliage and wood parameters of branches of 12-year-old loblolly pine (Pinus taeda L.) trees were characterized after 21 months of exposure to fertilizer, irrigation and elevated CO₂ treatments. Branches of loblolly pine trees were enclosed in plastic chambers and exposed to ambient, ambient +175 and ambient +350 umol mol^–1 CO₂ concentrations. Measurements of foliage and wood at the fascicle, flush and branch levels were made at the end of the 21 month study period. The +350 CO₂ treatment did not significantly increase fascicle radius or length but did increase the number of fascicles on the first flush. Fertilization significantly increased fascicle radius and length, while irrigation significantly increased number of fascicles and flush length of first flush. The +350 CO₂ treatment also significantly increased flush length of the first flush. Significant interaction of fertilization and irrigation with CO₂ was observed for fascicle length. Significant interactions of fertilization and irrigation were also observed for flush length, number of fascicles and fascicle length. Observed increases in fascicle radius, fascicle length, number of fascicles and flush length may have been responsible for the significantly higher flush leaf area observed for the all three treatments. Also, a combination of fertilization and irrigation increased leaf area by 82% compared to that in the control when averaged across CO₂ treatments. At the branch level +350 CO₂ treatment significantly increased shoot length but not the number of flushes on the branch. In general with the exception of bark density and total number of needle scales, neither fertilization nor irrigation had any significant effect on other branch level parameters. Results from this study indicate that with ‘global change’ an increase in CO₂ alone may increase leaf area via an increase in flush length and number of fascicles. Combining increases in CO₂ with fertilization and irrigation could greatly enhance leaf area which when coupled to observed increases in net photosynthesis as a result of elevated CO₂ could greatly increase productivity of loblolly pine trees. Received: 22 August 1996 / Accepted: 5 March 1997     

长期施肥制度对稻田土壤反硝化细菌群落活性和结构的影响

以中国科学院桃源农业生态试验站长期定位施肥试验为平台,研究了3种长期施肥制度(对照不施肥-CK,化学施肥-NPK,化学施肥+有机肥-NPKOM)下土壤反硝化速率的差异.同时,以硝酸还原酶基因(narG)作为反硝化细菌的功能标志物,分析了施肥对反硝化细菌群落结构和多样性的影响.结果表明,长期施用有机肥的土壤反硝化速率,反硝化菌多样性都高于对照和施用化肥处理.从3个处理的土壤样品中共获得35个narG基因的可操作分类单元(OTU)主要分布在两个簇,与变形菌门(Proteobacteria)和放线菌门(Actinobacteria)的反硝化细菌有一定的亲缘关系,均为首次从土壤中克隆.Shannon多样性指数显示,NPKOM处理的narG基因多样性最高,CK处理次之,NPK处理最低.LUBSHUFF软件对narG基因群落组成的分析显示,施有机肥后含narG基因的细菌群落组成与CK之间有显著性差异(P<0.05),而化肥(NPK)没有产生显著影响.实验结果为进一步研究亚热带地区水稻土反硝化作用及反硝化功能菌提供了重要的依据.     

Activity and composition of the denitrifying bacterial community respond differently to long-term fertilization

The objective of this study was to explore the long-term effects of different organic and inorganic fertilizers on activity and composition of the denitrifying and total bacterial communities in arable soil. Soil from the following six treatments was analyzed in an experimental field site established in 1956: cattle manure, sewage sludge, Ca(NO3)2, (NH4)2SO4, and unfertilized and unfertilized bare fallow. All plots but the fallow were planted with corn. The activity was measured in terms of potential denitrification rate and basal soil respiration. The nosZ and narG genes were used as functional markers of the denitrifying community, and the composition was analyzed using denaturing gradient gel electrophoresis of nosZ and restriction fragment length polymorphism of narG, together with cloning and sequencing. A fingerprint of the total bacterial community was assessed by ribosomal intergenic spacer region analysis (RISA). The potential denitrification rates were higher in plots treated with organic fertilizer than in those with only mineral fertilizer. The basal soil respiration rates were positively correlated to soil carbon content, and the highest rates were found in the plots with the addition of sewage sludge. Fingerprints of the nosZ and narG genes, as well as the RISA, showed significant differences in the corresponding communities in the plots treated with (NH4)2SO4 and sewage sludge, which exhibited the lowest pH. In contrast, similar patterns were observed among the other four treatments, unfertilized plots with and without crops and the plots treated with Ca(NO3)2 or with manure. This study shows that the addition of different fertilizers affects both the activity and the composition of the denitrifying communities in arable soil on a long-term basis. However, the treatments in which the denitrifying and bacterial community composition differed the most did not correspond to treatments with the most different activities, showing that potential activity was uncoupled to community composition.     

Nutrient uptake by intact and disturbed roots of loblolly pine seedlings

Most measurements of nutrient uptake use either hydroponic systems or soil-grown roots that have been disturbed by excavation. The first objective of this study was to test how root excavation affects nitrate uptake. Rates of NO₃^? uptake by mycorrhizal loblolly pine (Pinus taeda L.) seedlings were measured in intact sand-filled columns, hydroponics, and disturbed sand-filled columns. Total nitrate uptake in intact sand-filled columns was higher than in disturbed columns, indicating that disturbance lowers uptake. Transferring plants from the sand-filled columns to hydroponics had little effect on NO₃^? uptake beyond delaying uptake for an hour. The second objective of this study was to determine whether NH₄⁺, Ca²⁺, Mg²⁺ and K⁺ uptake could be studied using sand-filled columns, since previous studies had tested this method only for nitrate uptake. Uptake rates of NH₄⁺ and K⁺ were positive, while Ca²⁺ and Mg²⁺ uptake rates were negative in intact sand-filled columns, indicating that net efflux may occur even without physical disturbance to the root system. The sand-filled column approach has some limitations, but holds promise for conducting nutrient uptake studies with minimal disturbance to the root system.     

Seasonal development of loblolly pine lateral roots in response to stand density and fertilization

In 1989, two levels each of stand density and fertilization treatments were factorially established in a 9-year-old loblolly pine plantation on a P-deficient Gulf Coastal Plain site in Rapides Parish, Louisiana, USA. In 1995, a second thinning was conducted on the previously thinned plots and fertilizer was re-applied to the previously fertilized plots. The morphology of new long lateral roots was evaluated at 2-week intervals in five Plexiglas rhizotrons per plot of two replications. The overall objective of this study was to evaluate the seasonal initiation of six morphological categories of long lateral roots ( 2.5 cm in length) in response to stand density and fertilization. Lateral root development exhibited a seasonal pattern with the initiation of branched lateral roots predominantly occurring in spring and summer. The initiation of non-branched lateral roots occurred throughout the year regardless of season. Stand density did not affect lateral root morphological development. However, fertilization stimulated the initiation of branched lateral roots that were greater than 1 mm in diameter.     

Modeling magnesium,phosphorus and potassium uptake by loblolly pine seedlings using a Barber-Cushman approach

The Barber-Cushman mechanistic nutrient uptake model, which has been utilized extensively to describe and predict nutrient uptake by crop plants, was evaluated for its ability to predict K, Mg, and P uptake by loblolly pine (Pinus taeda L.) seedlings. Sensitivity analyses were also used to investigate the impact of changes in soil nutrient supply, root morphological, and root uptake kinetics parameters on simulated nutrient uptake. Established experimental techniques were utilized to define the 11 parameters needed to model uptake by 1-0 seedlings of K, Mg, and P from a modified A horizon soil (Lilly series). Model predictions of K and P uptake over a 180-d growth period were underestimated by 6 and 11%, respectively. Estimates of Mg uptake were underestimated by 62%. While the level of agreement between predicted and observed K and P values was quite acceptable, analysis of parameter values and results of sensitivity analyses both indicated that the model underestimation of Mg uptake was the result of applying an I_max value developed under relatively low Mg concentration to a situation in which the functional I_max would be much higher due to the dominance of passive versus active uptake. Overall results of sensitivity analyses indicate that under the circumstances investigated, I_max, was the primary variable controlling plant uptake of K, Mg, and P. The dominance of this term over others was due to the relatively high C_li values for all three nutrients. Reducing (-50%) or increasing (+ 100%) other soil supply, root morphological, and remaining root uptake kinetics values did not substantially alter model estimates of nutrient uptake.     

Comparative effects of four mycorrhizal fungi on loblolly pine seedlings growing in a greenhouse in a Piedmont soil

Summary A greenhouse study was conducted to evaluate the effect of ectomycorrhizae on loblolly pine (Pinus taeda L.) growing in a Piedmont soil. Pine seedlings were inoculated with one of four species of fungi (Scleroderma aurantium, Pisolithus tinctorius, Thelophora terrestris, andRhizopogon roseolus). The seedlings were grown in pots containing a Cecil sandy clay loam amended to create a gradient of extractable P ranging from 5.9 to 52.5 g/g. After ten months, all colonized seedlings were significantly larger than control seedlings. However, of the four fungi,Scleroderma aurantium mediated a far superior shoot growth response to increasing levels of soil P; the seedlings were significantly larger than those colonized by any other fungus and also had the largest root systems and greatest degree of mycorrhizal colonization.     

Gas exchange and canopy structure of 9-year-old loblolly pine,pitch pine and pitch x loblolly hybrids

Summary Seasonal gas exchange and canopy structure were compared among 9-year-old loblolly pine (Pinus taeda L.), pitch pine (Pinus rigida Mill.), and pitch x loblolly hybrids (Pinus rigida x taeda) growing in an F2 plantation located in Critz, Va., USA. Leaf net photosynthesis, conductance, internal CO₂ concentration (c_i), water use efficiency (WUE; photosynthesis/conductance), dark respiration and the ratio of net photosynthesis/respiration did not vary among or within the three taxa. Significant differences in volume production, crown length, total crown leaf surface area and the silhouette area of shade shoots among the taxa were observed. The loblolly-South Carolina source had greater volume and crown surface area than the pitch pine, and the hybrid taxa were intermediate between the two. Although the silhouette area ratio of shade foliage varied among taxa, it was not related to volume. A strong relationship between total leaf surface area and volume was observed. Leaf conductance, c_i, WUE and leaf water potential were the physiological parameters significantly and positively correlated with volume. This study suggests that the amount of needle surface in the canopy is more important in early stand volume growth than the leaf carbon exchange rate and the degree of needle self-shading in the lower canopy.     

Diurnal changes in allocation and partitioning of recently assimilated carbon in loblolly pine seedlings

We examined diurnal fluctuations in acquisition and partitioning of recently assimilated ¹⁴CO₂, and in subsequent allocation and partitioning to roots of loblolly pine (Pinus taeda L.) seedlings. Nonmycorrhizal seedlings were grown under optimal nutrient conditions in continuously flowin solution culture. Shoots of 15-week-old loblolly pine seedlings were labeled with ¹⁴CO₂ for 30 min at four separate labeling times: 1000, 1200, 1400 and 1600 h. Six whole plant harvests were conducted during a 48 h chase period, i.e. 0, 4, 8 12, 24 and 48 h after the end of the labeling and evacuation periods. Although assimilation of ¹⁴CO₂ was constant between 1000 and 1400 h, there were significant differences in partitioning of ¹⁴C-labeled assimilate in needles of all age classes. The highest percentage of recently assimilated ¹⁴CO₂ in the ethanol-soluble fraction of photosynthesizing tissue was observed near the beginning and end of the photoperiod. Partitioning of ¹⁴C in the ethanol-soluble fraction declined between the 1000 and 1400 h labeling eriods, and was accompanied by an increase in partitioning of recently assimilated ¹⁴CO₂ toward starch and a decrease in respiratory losses. These data suggest that most of the ¹⁴CO₂ assimilated at 1000 h was used to support shoot metabolic activities and possibly restore soluble sugar reserves. Peak starch accumulation in needles during the 1400 h labeling period, concomitant with minimal respiratory loss, indicated that photosynthate production exceeded demand and export out of source leaves. A possible feedback regulation of photosynthesis by starch and/or sugar accumulation may be responsible for the observed decline in assimilation of ¹⁴CO₂ during the 1600 h labeling period. Net accumulation of recently assimilated ¹⁴CO₂ in roots was correlated with assimilation rate of ¹⁴CO₂, but independent of partitioning of recently assimilated carbon in photosynthetic tissue. However, the percentage of total seedling ¹⁴C allocated to roots was essentially the same throughout the 48 h chase, regardless of time of labeling and assimilation rate. The data suggest a strong diurnal regulation of starch and soluble sugars synthesized from recently assimilated carbon in needles of loblolly pine seedlings that was independent of assimilation rate. Allocation and transport of recently assimilated carbon to roots of loblolly pine seedlings were not subject to short-term fluctuations in supply and demand.     

Soil bacterial diversity in a loblolly pine plantation: influence of ectomycorrhizas and fertilization

We studied the effect of ectomycorrhizas and fertilization on soil microbial communities associated with roots of 10-year-old loblolly pine. Ectomycorrhizas were identified using a combination of community terminal restriction fragment profiling and matching of individual terminal restriction fragments to those produced from ectomycorrhizal clones and sequences recovered from roots and sporocarps. Differences between bacterial communities were initially determined using cluster analysis on community terminal restriction fragment profiles and through subsequent recovery of 16S rDNA clones. Analysis of bacterial clones revealed that terminal restriction fragment length was often shared between taxonomically dissimilar bacterial types. Consequently, we could not reliably infer the identity of peaks in the bacterial community profile with some exceptions, notably chloroplast rDNA that generated an approximate peak size of 80.2 bp. Fertilization increased the frequency of a Piloderma-like ectomycorrhiza. However, we did not detect clear effects of fertilization or the presence of viable ectomycorrhizas on bacterial communities. Bacterial communities seemed to be determined largely by the carbon and nitrogen content of soil. These results suggest that important soil microbial groups respond differently to soil conditions and management practices, with ectomycorrhizal communities reflecting past nutrient conditions and bacterial communities reflecting current environmental conditions of soil microsites.     

Seeds and seedlings of two neotropical montane understory shrubs respond differently to anthropogenic edges and treefall gaps

Edges resulting from forest clear-cutting and treefall gaps can affect plant populations and consequently the distribution of species across landscapes. These two types of disturbance might interact to exacerbate or ameliorate “edge effects”, a rarely tested possibility. We focused on the effects of distance from forest edge (0–10, 30–40, 60–70, and 190–200 m) and habitat within forest fragments (treefall gaps and intact forest) on the early stages of development of Palicourea gibbosa and Faramea affinis, two common shrubs of montane forests in southwest Colombia. Seed germination and seedling growth did not change with distance from forest edge. Within forest fragments, however, seed germination and seedling growth were higher in treefall gaps than in intact forest understory for both species. In contrast, seed predation was influenced by distance from forest edge and in P gibbosa it depended on habitat. Seed predation was highest in the forest interior (190–200 m from forest edge) and in P. gibbosa this was true only in treefall gap habitats. These results suggest that animal mediated processes such as post-dispersal seed predation are more likely than physiological processes to be affected by anthropogenic edges. Our results provide some evidence that treefall gaps may interact with “edge effects”, however, they are inconclusive as to whether they exacerbate or ameliorate them. Received: 31 August 1998 / Accepted: 18 February 1999     

Photosynthesis and transpiration of monterey pine seedlings as a function of soil water suction and soil temperature

Rates of photosynthesis, respiration, and transpiration of Monterey pine (Pinus radiata D. Don) were measured under controlled conditions of soil water suction and soil temperature. Air temperature, relative humidity, light intensity, and air movement were maintained constant. Rates of net photosynthesis, respiration, and transpiration decreased with increasing soil water suction. The decrease in the rates of net photosynthesis and transpiration as a function of the soil temperature at low soil water suctions may be attributed to changes in the viscosity of water. At soil water suctions larger than 0.70 bars rates of transpiration and net photosynthesis may be affected in the same proportion by changes in stomatal apertures.